The present invention generally relates to display devices for magnetic tape recording and/or reproducing apparatuses which record and/or reproduce a signal onto and/or from a traveling magnetic tape, and more particularly to a display device which is designed to display a travel quantity of the magnetic tape in real-time.
Conventionally, as systems for displaying the travel quantity of a magnetic tape in a recording and/or reproducing apparatus which employs the magnetic tape, such as a video tape recorder (VTR), there were the following three systems, for example. According to a first system, the rotations of reel discs are detected, and the display of the tape travel quantity is carried out according to the rotational speeds of the reel discs. According to a second system, a tape counting roller is provided exclusively for detecting the tape travel within a tape driving system, and the tape travel quantity is displayed by detecting the rotation of this tape counting roller. Further, according to a third system, the tape travel quantity is displayed by detecting a signal which has been recorded on the tape. However, in each of these conventional systems, there were the following disadvantages.
The first system detects the rotational speeds of both the reel discs. Detection signals indicative of the respective rotational speeds of the reel discs, are processed in a microprocessor and the like according to predetermined calculating equations, and the tape travel quantity is displayed in real-time. Thus the cost of the apparatus became high. Moreover, there was a disadvantage in that the predetermined calculating equations to which the processing of the detection signals is based, had to be changed according to the diameter of the reel hubs, and adjustments were consequentially required in the microprocessor and the like which carried out the processing.
The second system was disadvantageous in that the tape counting roller had to be provided in the tape driving system, exclusively for detecting the tape travel. Further, it was essential that there was no slippage between the tape and the tape counting roller, in order to provide an accurate display of the tape travel quantity. For this reason, the angular range over which the tape is wrapped around the tape counting roller, had to be large so as to prevent the slippage between the tape and the tape counting roller. However, this wrapping of the tape around the tape counting roller over a large angular range, reduced the degree of freedom with which the tape path can be designed. Further, the dimensions of the tape counting roller had to be exact, and the tape counting roller had to be assembled with high precision.
The application of the third system was quite limited, because this third system could not be employed in a case where the signal which is used for detecting the tape travel quantity was not recorded on the tape.